The invention relates to a method for manufacturing a lifting hook billet comprising a hook portion and a base portion.
The invention also relates to a lifting hook comprising a hook portion, a shaft integrated to the hook portion, a supporting portion at the end of the shaft substantially coaxial with the shaft, the diameter of the supporting portion exceeding the diameter of the shaft, and the supporting portion including a first bearing surface surrounding the shaft and facing the hook portion.
Lifting hooks are used in different hoisting apparatuses for supporting a load. In order to be able to turn a load as desired or to turn a hook to an appropriate position regarding the load, the hook is suspended from its upper end to a separate supporter rotatably around the vertical axis. At present the hook is frequently pivoted in order for the hook to rotate smoothly even when carrying a heavy load. Highly complicated constructions are presently used to mount the hook into a hole in the body rotatably in relation to the body. Both the hook and the body require a separate bearing surface supporting the load, which in today""s heavy hoisting use is made of various separate bearing surfaces and fastening portions. Such surfaces are disclosed in publications DE 72 51 114 and DE 37 35 021, for example. U.S. Pat. No. 3,995,822 in turn discloses a solution in which the hook is at first fabricated so that a supporting flange is placed at the upper end of the hook, where after a supporting portion is cast around the hook between the flange and the hook portion around the axis of the hook. This structure is intended for solutions in which the hook carries a small load. Here it is not possible either to form proper bearing surfaces, since the cast portion cannot in practice be machined around the hook on location.
The problem with prior art solutions is that the constructions composed of different separate portions are expensive to manufacture. Possible mounting mistakes and the loading capacity of small components restrict the loading and may cause the construction to collapse. This, in turn, increases the accident risk.
It is an object of the present invention to provide such a method for manufacturing a lifting hook and such a lifting hook that allow to avoid the problems of the prior art solutions and to provide a firm and durable hook construction. The method of the invention comprises the steps of forming a lifting hook shaft from the base portion of the lifting hook billet, forming a first bearing surface at the end of the lifting hook shaft, the first bearing surface faces the hook portion and is intended to support the lifting hook, and forming a uniform bearing ring around the lifting hook shaft, the bearing ring being arranged between the first bearing surface and the hook portion, by detaching it from the lifting hook billet. The lifting hook of the invention further comprises a uniform bearing ring surrounding the shaft, the bearing ring being arranged between the supporting portion and the hook portion, the bearing ring being made of a hook billet by detaching a ring-shaped portion that surrounds the hook shaft.
The basic idea with the invention is that the supporting portion at the end of the lifting hook as well as both the bearing surfaces of the lifting hook are formed of the same hook billet so that, on one hand the supporting portion at the upper end of the hook supporting the load and the bearing surface on the lower surface thereof are made of the same material as the rest of the hook, and on the other hand the lower bearing ring supporting the hook and the bearing surface on the upper surface thereof are machined of the same hook billet, in which case the required bearings can be placed between these two bearing surfaces. Thus a uniform solid bearing surface is simply and easily obtained at the upper end of the hook and beneath the hook. The structure is also very reliable and endures heavy loading. Another advantage is that the supporting body does not require a bearing surface, instead the bearing ring detached from the hook by machining is unrotatably supported by the body.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.